Negotiation Mode; Keep Alive; Remote Dns Server - ZyXEL Communications P-793H User Manual

• Set the IPSec SA lifetime. This field allows you to determine how long the IPSec
SA should stay up before it times out. The P-793H v2 automatically renegotiates
the IPSec SA if there is traffic when the IPSec SA lifetime period expires. The P-
793H v2 also automatically renegotiates the IPSec SA if both IPSec routers have
keep alive enabled, even if there is no traffic. If an IPSec SA times out, then the
IPSec router must renegotiate the SA the next time someone attempts to send
traffic.

11.9.6 Negotiation Mode

The phase 1 Negotiation Mode you select determines how the Security
Association (SA) will be established for each connection through IKE negotiations.
• Main Mode ensures the highest level of security when the communicating
parties are negotiating authentication (phase 1). It uses 6 messages in three
round trips: SA negotiation, Diffie-Hellman exchange and an exchange of
nonces (a nonce is a random number). This mode features identity protection
(your identity is not revealed in the negotiation).
• Aggressive Mode is quicker than Main Mode because it eliminates several
steps when the communicating parties are negotiating authentication (phase 1).
However the trade-off is that faster speed limits its negotiating power and it also
does not provide identity protection. It is useful in remote access situations
where the address of the initiator is not know by the responder and both parties
want to use pre-shared key authentication.

11.9.7 Keep Alive

When you initiate an IPSec tunnel with keep alive enabled, the P-793H v2
automatically renegotiates the tunnel when the IPSec SA lifetime period expires
(see Section 11.9.5 on page 184
IPSec tunnel becomes an "always on" connection after you initiate it. Both IPSec
routers must have a P-793H v2-compatible keep alive feature enabled in order for
this feature to work.
If the P-793H v2 has its maximum number of simultaneous IPSec tunnels
connected to it and they all have keep alive enabled, then no other tunnels can
take a turn connecting to the P-793H v2 because the P-793H v2 never drops the
tunnels that are already connected.
When there is outbound traffic with no inbound traffic, the P-793H v2
automatically drops the tunnel after two minutes.

11.9.8 Remote DNS Server

In cases where you want to use domain names to access Intranet servers on a
remote network that has a DNS server, you must identify that DNS server. You
P-793H v2 User's Guide
for more on the IPSec SA lifetime). In effect, the
Chapter 11 VPN
185